1. Field of the Invention
The present invention relates, in general, to the inspection of tubulars, and more specifically to systems, devices, and methods for inspecting a body of a tubular using an electro-magnetic acoustic transducers.
2. Description of the Related Art
A drilling riser is a conduit that provides an extension of a subsea oil well to a surface drilling rig. Drilling risers are made up of pipe joints bolted together with flanges. Each joint is typically 18-24 inches in diameter and 70-100 feet in length, and can exceed one inch in wall thickness, which is considered a heavy wall. Normally, there are longitudinal and transverse welds in a joint. Over time of usage, a riser joint may develop wall thinning, corrosion, pitting, and cracks with various orientations on the interior and exterior surfaces. It may also contain mill defect such as delamination that, due to cyclic fatigue when in service, have grown beyond the maximum permissible size in new riser material.
Today, the offshore operators are strongly committed to protecting the environment. Pigging and riser inspection are performed periodically to determine the condition of the installation and the riser in particular. Such inspection plays a key role in ensuring the integrity, safety and security of the riser pipes.
For drilling riser joint type of pipes, the outer surface, however, is normally covered by a buoyancy jacket and possibly coated with an epoxy. Additionally, auxiliary lines, for example, for choke, kill, and hydraulic purposes, may be mounted off the center around the central riser pipe and being parallel to the pipe axis. Inspection from the outside requires removing the auxiliary lines, the buoyancy jacket and epoxy, and thus, is time consuming, cost prohibitive and impractical. Inspection from the inside, however, is more practical and can provide full coverage over the entire length of the riser joints.
There are several existing Non-destructive Testing (NDT) methods that can be employed in riser pipe inspection. Among them, conventional Ultrasonic Testing (UT) inspection method requires a couplant and a reasonably clean surface for good coupling of ultrasonic energy into the inspected material. The Magnetic Flux Leakage (MFL) inspection method needs to magnetize the inspected material to near magnetic saturation. Thus, it is not effective on heavy wall thicknesses. Moreover, the magnetic permeability within a typical weld seam varies drastically, making MFL impractical for weld inspection. The Eddy Current (EC) inspection method has limited depth of penetration, and thus, can only detect surface or near surface defects. Other NDE methods that are commonly used in the field, e.g. Magnetic Particle Testing (MT) and Penetrant Testing (PT), are slow due to the manual processes involved and require access to the surface being inspected. The remote field EC (RFEC) method is used for Outer Diameter (OD) and Inner Diameter (ID) defect detection and sizing. It has been used up to at least 15 mm wall and could possibly be used for thicker wall. Likely problems, however, are speed and sensitivity, but new signal processing methods should help in this area.
A riser pipe inspection job typically includes measuring the wall thickness and detecting on the ID or OD of the main body any longitudinal and transverse cracks, corrosion, and pitting. In addition, the inspection should be able to detect longitudinal and transverse weld imperfections, such as cracks, lack of fusion, and porosity, and subsurface defects such as delamination. This represents a situation where many types of defects need to be detected in one scan by one inspection tool. A thorough inspection in this situation requires a combination of multiple NDT techniques, such as UT, MFL, MT, and PT, and possibly multiple tools. Such combined inspections are usually economically prohibitive.
Electromagnetic acoustic transducer (EMAT) inspection techniques for non-contact ultrasound generation and reception have been used in some industrial applications. The inventors have recognized that EMAT has certain advantages over the above described industry-accepted techniques. For example, EMAT techniques can provide the benefits that the UT technique has to offer, e.g. the superior depth of penetration for flaw detection or measurement, but is better than UT due to the non-contact nature and no-couplant requirement capability. Also recognized is that the EMAT technique has less stringent requirements on surface cleaning and allows faster inspection speed.
Accordingly, recognized by the inventors is the need for systems, devices (tools), and methods for inspecting a body of the tubular such as a riser pipe, that can leverage advantages of EMAT with an innovative, with a tool/device containing multiple tightly packed high-performance EMAT configurations to detect the wide range of defects that may be encountered in a typical tubular inspection, and to provide 100% coverage of the inner diameter and outer diameter surfaces and the volume in between, over the entire length of the pipe being inspected even when the inner diameter of the pipe changes due to deformation of the pipe or buildup of particulate matter.